Binary zeolitic systems, their synthesis and their utilization

Abstract

The present invention concerns binary zeolitic systems comprising two zeolites A and B having different crystalline structures while having common structural units. The crystals of the zeolite A form a central core surrounded by a crown of crystals of zeolite B, the zeolites A and B being disposed concentrically and following the same longitudinal axis. These systems are formed by the introduction of a nucleation gel containing germs of the zeolite A in a growth gel where the crystallization parameters are favorable to the crystallization of the zeolite B. The binary zeolitic systems are useful as catalysts for transforming hydrocarbons and more especially as cracking catalysts.

What is claimed is: 
     
       1. A method for the catalytic cracking of a hydrocarbon feed to transfer it essentially into gasoline, gas and hydrogen, which comprises contacting said hydrocarbon feed with a catalytically effective cracking amount of catalyst wherein the catalyst is a binary zeolitic system comprised of zeolites, A and B, having different crystalline structures while having common structural units, wherein the crystals of the zeolite A forming a central core are selected from the group consisting of offretite and omega zeolite and are surrounded by a crown or ring of crystals of zeolite B, which are selected from the group consisting of omega zeolite and mordenite, the zeolites A and B being disposed concentrically and following the same longitudinal axis, and thereafter recovering gasoline, gas and hydrogen. 
     
     
       2. The method of claim 1, wherein the hydrocarbon feed is a petroleum cut. 
     
     
       3. A method for increasing the yield of gasoline from the catalytic cracking of a petroleum cut, which comprises contacting said petroleum cut with a catalytically effective cracking amount of a catalyst, wherein the catalyst is a binary zeolitic system comprised of zeolites, A and B, having different crystalline structures while having common structural units, wherein the crystals of the zeolite A forming a central core are selected from the group consisting of offretite and omega zeolite and are surrounded by a crown or ring of crystals of zeolite B, which are selected from the group consisting of omega zeolite and mordenite, the zeolites A and B being disposed concentrically and following the same longitudinal axis, and thereafter recovering said gasoline.